There’s a few components that controls the engine idle speed.
The first is the idle air control valve.
Sometimes removing the IAC valve and cleaning it with throttle body cleaner will fix an idle problem. Other times the IAC valve requires replacement.
The IAC valve is also controlled by the PGM/FI relay.
These relays have been known to be a problem on Honda’s.
There’s also the starting air valve.
So basically, you’re going to need a factory service manual that explains how to test these components, along with the equipment to do so.
Because you don’t want to just throw parts/money at the problem.